源自Ni-Nb共晶团簇式的Ni-Nb-(Zr,Ta,Ag)三元块体非晶合金成分设计

COMPOSITION DESIGN OF Ni-Nb-(Zr,Ta,Ag) TERNARY BULK METALLIC GLASSES BASED ON CLUSTER FORMULA OF Ni-Nb EUTECTIC

利用团簇+连接原子模型设计Ni-Nb基三元块体非晶成分.首先,解析出二元共晶点Ni_(59.5)Nb_(40.5)的团簇式[(Ni_(0.5)Nb_(0.5))-Ni_6Nb_6]Ni_3,其中,(Ni_(0.5)Nb_(0.5))Ni_6Nb_6为源自Ni_6Nb_7(Fe_7W_6型)共晶相的以(Ni_(0.5)Nb_(0.5))为心的二十面体团簇.相应的,具有最大非晶形成能力的Ni-Nb二元成分Ni_(62)Nb_(38)可描述成团簇式[Ni-Ni_6Nb_6]Ni_3,此时,二十面体团簇的中心位置完全由Ni占据.以[Ni-Ni_6Nb_6]Ni_3二元非晶团簇式为基础,通过引入第3组元Zr,Ta或Ag,设计出具有更高非晶形成能力的Ni-Nb-(Zr,Ta,Ag)三元合金,利用水冷铜模吸铸方法获得临界直径为3 mm的块体非晶.热分析和力学测试表明这些三元块体非晶具有较高的热稳定性,其中[Ni-Ni_6Nb_5Ta]Ni_3具有最高的玻璃转变温度T_g(935 K)和晶化温度T_x(952 K);这些三元块体非晶具有一定的塑性变形能力(延伸率约为0.3%),[Ni-Ni_6Nb_5Zr]Ni_3和[Ni-Ni_6Nb_5Ta]Ni_3块体非晶的压缩断裂强度分别达到3.2和3.4 GPa.

A cluster-plus-glue atom model was employed to design Ni-Nb based ternary bulk metallic glasses.The binary eutectic point Ni_（59.5）Nb_（40.5） was first interpreted by the model in form of a cluster formula[（Ni_（0.5）Nb_（0.5））-Ni_6Nb_6]Ni_3,where the cluster is（Ni_（0.5）Nb_（0.5））-centered icosahedron derived from a eutectic phase Ni_6Nb_7（Fe_7W_6 type）.It was then pointed out that the best binary glass former Ni_（62）Nb_（38） could be interpreted based on the eutectic cluster formula by replacing the cluster center Nb_（0.5） with Ni_（0.5,namely[Ni-Ni_6Nb_6]Ni_3=Ni_（62.5）Nb_（37.5）.To further improve the glass-forming ability,Zr,Ta and Ag are selected as alloying additions to partially replace Nb in the[Ni-Ni_6Nb_6]Ni_3 cluster formula,and glassy rods with a critical size of 3 mm are achieved at appropriate ternary compositions by copper-mould suction-casting.DTA measurements indicate these bulk metallic glasses exhibit high thermal stabilities,among which the[Ni-Ni_6Nb_5Ta]Ni_3 alloy has the highest T_g（glass transition temperature）of 935 K and T_x（crystallization temperature） of 952 K. Room-temperature compressive curves of[Ni-Ni_6Nb_5Zr]Ni_3 and[Ni-Ni_6Nb_5Ta]Ni_3 alloys show they have limited plasticity with a elongation of about 0.3%,fracture strength of the[Ni-Ni_6Nb_5Zr]Ni_3 and [Ni-Ni_6Nb_5Ta]Ni_3 BMGs are about 3.2 GPa and 3.4 GPa,respectively.